The siphuncle was broad and positioned ventrally in the shell, which ranged in shape from cyrtoconic brevicones (curved and short) to rare orthoconic longicones (straight and long).

In both bisonocerids and endocerids, the endosiphuncular deposits are conical in shape ("endocones"), concreted from the rim of the siphuncle and tapering towards the apex of the shell.

Both orders possess simple perforate endocones, with a hole at the tip of each cone for siphuncle tissue to pass through.

Structures similar to simple endocones are also apparently present in some members of the earlier cephalopod orders Yanhecerida and Ellesmerocerida.

Bisonocerids appear to be oncomyarian, meaning that they have a numerous small, undifferentiated muscle scars ringing around their body chamber.